The present invention relates to novel pyrazoloneazo pigments of the general formula I 
where R1, R2, R3 and R4 are independently hydrogen, chlorine, methyl or ethyl subject to the proviso that at least one of R1 to R4 is not hydrogen,
characterized by a CIELAB hue angle of from 80 to 85xc2x0, a chroma of from 58 to 62 and a lightness of xcex887 (45xc2x0 measuring angle, D65 illuminant).
The invention further relates to the preparation of these pigments and to their use for coloring macromolecular organic materials and also to macromolecular organic materials colored with these pigments.
Pyrazoloneazo pigments are used as yellow pigments for coloring plastics, as will be known. EP-A-263 074 discloses mixed crystals of laked azo dyes of the pyrazolone series that contain two different laking cations. True, mixed Ca-Na crystals are described, but these pigments have an orange hue and the color strength and transparency of their colorations lack conviction.
It is an object of the present invention to provide pyrazoloneazo pigments for the greenish yellow hue sector which are notable for altogether advantageous application properties, including especially the color strength and transparency of their colorations.
We have found that this object is achieved by the pyrazoloneazo pigments I defined at the beginning.
The present invention further provides a process for preparing these pyrazoloneazo pigments I, which comprises diazotizing a 2-aminobenzenesulfonic acid of the general formula II 
in an aqueous medium with sodium nitrite, coupling the resulting diazo component in an aqueous medium with a 1-(3xe2x80x2-sulfophenyl)-3-methyl-5-pyrazolone of the general formula III 
and then reacting the coupling product with an aqueous solution of a calcium salt in the presence of an anionic surfactant to form a mixed sodium-calcium salt and then isolating the latter in a conventional manner.
The present invention further provides for the use of the pyrazoloneazo pigments I for coloring macromolecular organic materials.
R1 to R4 in the formula I are independently hydrogen, chlorine, methyl or ethyl subject to the proviso that at least one of R1 to R4 is not hydrogen. Preferably R1 and R2 are not hydrogen and particularly preferably R1 and R2 are each chlorine and R3 and R4 are each hydrogen.
The pyrazoloneazo pigments I according to the invention have a greenish yellow hue (CIELAB hue angle from 80 to 85xc2x0) having excellent cleanness (Chroma 58 to 62). They have a high color strength and are notable for the transparency of their colorations in macromolecular organic materials. They are present in the form of acicular crystals (length about 0.8-2.5 xcexcm, thickness about 0.1-0.2 xcexcm), which are convenient to incorporate into application media.
The pyrazoloneazo pigments I are advantageously preparable by the process of the invention, which in the presence of water as reaction medium is preferably carried out as a one-pot reaction without isolation of intermediates.
The first step of the process according to the invention is the diazotization of 2-aminobenzenesulfonic acid II with sodium nitrite.
It is customary to use from 1 to 1.1 mol of sodium nitrite per mole of 2-aminobenzenesulfonic acid II.
The diazotization is customarily carried out at a pH in the range from 0.5 to 0.8, which is set by addition of an aqueous acid, especially a mineral acid such as hydrochloric acid, and at from 0 to 5xc2x0 C.
The second step of the process according to the invention is the coupling of the resulting diazo component with the 1-(3xe2x80x2-sulfophenyl)-3-methyl-5-pyrazolone III (coupling component) in an aqueous medium.
This is customarily done in the presence of a buffer, for example sodium acetate, which is used to set a pH in the range from 4.8 to 5.1.
The reaction temperature is generally in the range from 15 to 20xc2x0 C.
The molar ratio of diazo component to coupling component III is generally in the range from 0.9:1 to 1:1.
The third step of the process according to the invention, the laking to form the mixed sodium-calcium salt, is carried out directly in the as-coupled reaction mixture in the presence of an anionic surfactant.
Useful surfactants include not only carboxylates, sulfates, phosphonates and phosphates but especially sulfonates, in particular alkanesulfonates, i.e., salts of alkanesulfonic acids. These are the sulfochlorination or sulfoxidation products of straight-chain paraffins, i.e., mixtures of homologous alkanes having from 12 to 18 carbon atoms.
It is customary to use from 100 to 180 g, preferably from 140 to 160 g, of surfactant per mole of coupling component III.
The laking is preferably carried out at from 75 to 85xc2x0 C., especially at about 80xc2x0 C.
Useful laking agents include in principle all water-soluble calcium salts. Examples are calcium chloride and calcium acetate, of which calcium chloride is preferred.
The laking product is then preferably subjected to a thermal treatment at from 90 to 95xc2x0 C. for the ultimate finishing of the particles.
The preparation process of the invention is conveniently carried out as follows:
The diazotizing step is carried out by dissolving the 2-aminobenzenesulfonic acid II in an alkaline aqueous medium, adding an acid to set a strongly acidic pH, adding ice to cool to about 0-5xc2x0 C. and then adding a sodium nitrite solution. Following a subsequent stirring time of about 1-2 h at this temperature, any excess nitrite still present is destroyed with amidosulfonic acid.
The coupling step is carried out by preparing an aqueous solution of the coupling component 1-(3xe2x80x2-sulfophenyl)-3-methyl-5-pyrazolone III by adding a buffer and then cooling to about 10-15xc2x0 C. by adding an ice-water mixture. The reaction mixture obtained in the diazotization is then added with rapid stirring and the temperature of the mixture is maintained at 15-20xc2x0 C.
After the coupling reaction has ended, the anionic surfactant is added, the mixture is heated to 75-85xc2x0 C. over about 0.5-1.5 h and then the laking agent is added over about 10-30 min with rapid stirring.
To finish the pigment particles, the reaction mixture is then heated to 90-95xc2x0 C. over about 10-30 min and subsequently stirred at that temperature for about 1-3 h.
The mixed sodium-calcium salt may be isolated in a conventional manner after cooling to about 60-65xc2x0 C. by addition of an ice-water mixture, filtration, washing with hot water and drying.
The pyrazoloneazo pigments I according to the invention are very useful for coloring macromolecular organic materials, for example cellulose ethers and esters such as ethylcellulose, nitrocellulose, cellulose acetate and cellulose butyrate, natural resins and synthetic resins such as addition polymerization resins and condensation resins such as aminoplasts, especially urea- and melamine-formaldehyde resins, alkyd resins, phenolic resins, polycarbonates, polyolefins, polystyrene, polyvinyl chloride, polyamides, polyurethanes, polyesters, acrylonitrile-butadiene-styrene rubbers, polyphenylene oxides, natural rubber, casein, silicone and silicone resins.
When used for this purpose, the pyrazoloneazo pigments I are notable for their greenish yellow hue, the cleanness of their hue and their color strength and also the transparency of their coloration, which are each substantially above the values obtained with the mixed crystals of EP-A-263 074.